In order to be able to properly mount a dental prostheses such as a bridge or a crown the teeth must be accurately filed down to frustoconical stumps having no undercuts. In addition it is necessary that each tooth stump be centered on an axis parallel to the axes of the adjacent stumps so that the part being installed can be slipped on parallel to these axes.
A positive dental model of the jaw portion with the ground-down tooth stumps is typically examined by the technician to check for undercuts or nonparallel stumps. Clearly the quality of such a visual examination depends on the experience of the person doing it.
It is also known to test for parallelism by running a sensing finger of a special testing apparatus around each stump. Not only is this system fairly complex and does it require expensive equipment, but it is relatively crude, not picking up small variations. In addition to the high cost, the stumps in the patient's mouth must frequently be reworked before the bridge or crown can be installed. In addition it is often necessary to diagnose whether when teeth are missing there is room available once the teeth have been reworked. To date the dental models are measured by means of calipers and the necessary sizes are calculated separately.
Digital calipers are known which are connected to a personal computer to take the necessary measurements. The accuracy of this procedure is also inadequate. Measuring teeth arches is not possible, so this measurement is traditionally done by lying a wire on the teeth and subsequently measuring the rectified length of the wire.